Australian authorities told 40,000 people to evacuate to higher ground on Thursday as a storm system generated by a powerful cyclone that pummelled the northeast two days ago swept down the coast with heavy rain.

Cyclone Debbie hit as a Category 4 storm in the north of tropical Queensland state on Tuesday, smashing tourist resorts, bringing down power lines, flattening canefields and shutting down coal mines.

Driving rain fell most heavily on Thursday in hinterland and coastal areas either side of the state capital, Brisbane.

"This severe weather system that began with Cyclone Debbie and is tracking down the coast is causing havoc across our state," Queensland Premier Annastacia Palaszczuk told reporters in Brisbane.

The cyclone was downgraded to a tropical low on Wednesday but it was driving squalls with torrential rain across a 1,200-km stretch of Australia's east coast, swelling rivers and prompting widespread flood warnings.

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Australian Prime Minister Malcolm Turnbull looks at damaged and flooded areas near Bowen, Queensland on Wednesday from aboard an Australian Army helicopter after Cyclone Debbie passed through the area earlier in the week. (Gary Ramage/Reuters)

In Lismore in the north of neighbouring New South Wales state, the State Emergency Service told residents to leave because weather forecasts predicted the town's worst flood in nearly 20 years.

The rural hub in the Northern Rivers region of New South Wales is home to at least 25,000 people.

Road fatality attributed to Debbie

Further north, Queensland's government closed more than 2,000 schools as sustained heavy rainfall brought flash floods to the Gold Coast tourist area and Mackay further north. In the cyclone-hit tropical north, the poor weather has slowed what was expected to be a lengthy clean-up operation.

Military helicopters, ferries and planes brought hundreds of holidaymakers stranded on resort islands in the storm's path to the mainland, where tens of thousands more people were still without power.

Cyclone Debbie floods

A car is in flood waters nearly past its tires Thursday in Murwillumbah, Australia. Heavy rain and flash flooding are hitting southeast Queensland and northern New South Wales as as ex-cyclone Debbie makes its way south across the country. (Jason O'Brien/Getty Images)

Resorts along the world-famous Great Barrier Reef and the Whitsunday coast bore the brunt of the storm on Tuesday with wind gusts stronger than 260 kph.

About 2,500 insurance claims have been filed but Queensland's top two insurers, Suncorp Group Ltd and RACQ, said it was too early to put a dollar figure on the damage.

One female tourist was killed in a car crash on Monday that police said was due to wild weather as Cyclone Debbie approached. Another two people were injured as the storm passed through.